Vector Displacement not showing same result as the mask of it
I can't be sure this is your problem without seeing a bit more of your shader-tree, but..
There's a difference between Generated-space and Object-space coordinates, where render-time displacement is concerned.

The Generated coordinates of mesh elements are evaluated before
displacement. (They measure 0-1 along the sides of the bounding-box of
the (unscaled) object, irrespective of its size, oriented with the
object's local axes.)
The Object coordinates of mesh elements are evaluated after
displacement. (They are measured in Blender Units from the (unscaled)
object's origin, along the object's local axes.)

Both sets of coordinates translate, rotate, and scale with their objects.
So, in this cube being displaced to a sphere, with the same 3D texture, a grid of cubic cells with thin walls:

On the left, the Generated coordinates are evaluated in the original state of the cube, and displace along with it, 'sticking' to the surface of the deforming object.
On the right, the Object coordinates of shading-points are evaluated after displacement, so the
deforming surface 'swims' through Object space.
So, for example, if you're making masks for displacement, and want to see where they wind up on the displaced surface, it's much easier to work in Generated space. I put mine in a group that I can re-use around the tree, offset so the origin is at the center of the bounding box, and ready-separated, to avoid too many Separate XYZ 's and spaghetti: